将一系列父子关系转换为层次树？

这需要一个非常基本的递归函数来将子/父对解析为树结构，并需要另一个递归函数来将其打印出来。只有一个函数就足够了，但是为了清楚起见，这里有两个（可以在此答案的末尾找到一个组合函数）。

首先初始化子对/父对对的数组：

$tree = array(    'H' => 'G',    'F' => 'G',    'G' => 'D',    'E' => 'D',    'A' => 'E',    'B' => 'C',    'C' => 'E',    'D' => null);

然后将数组解析为分层树结构的函数：

function parseTree($tree, $root = null) {    $return = array();    # Traverse the tree and search for direct children of the root    foreach($tree as $child => $parent) {        # A direct child is found        if($parent == $root) { # Remove item from tree (we don't need to traverse this again) unset($tree[$child]); # Append the child into result array and parse its children $return[] = array(     'name' => $child,     'children' => parseTree($tree, $child) );        }    }    return empty($return) ? null : $return;    }

和遍历该树以打印出无序列表的函数：

function printTree($tree) {    if(!is_null($tree) && count($tree) > 0) {        echo '<ul>';        foreach($tree as $node) { echo '<li>'.$node['name']; printTree($node['children']); echo '</li>';        }        echo '</ul>';    }}

以及实际用法：

$result = parseTree($tree);printTree($result);

这是内容

$result

Array(    [0] => Array(        [name] => D        [children] => Array( [0] => Array(     [name] => G     [children] => Array(         [0] => Array(  [name] => H  [children] => NULL         )         [1] => Array(  [name] => F  [children] => NULL         )     ) ) [1] => Array(     [name] => E     [children] => Array(         [0] => Array(  [name] => A  [children] => NULL         )         [1] => Array(  [name] => C  [children] => Array(      [0] => Array(          [name] => B          [children] => NULL      )  )         )     ) )        )    ))

如果需要更高的效率，可以将这些功能合并为一个，并减少迭代次数：

function parseAndPrintTree($root, $tree) {    $return = array();    if(!is_null($tree) && count($tree) > 0) {        echo '<ul>';        foreach($tree as $child => $parent) { if($parent == $root) {   unset($tree[$child]);     echo '<li>'.$child;     parseAndPrintTree($child, $tree);     echo '</li>'; }        }        echo '</ul>';    }}

您只会在这样小的数据集上保存8次迭代，但在较大的数据集上可能会有所作为。